Our discovery of a new protein in bone, osteocalcin, containing the vitamin K dependent calcium-binding amino acid, gamma-carboxyglutamate (Gla), and the presence of a vitamin K carboxylase enzyme system in bone microsomes indicates an important functional role for vitamin K in bone metabolism. Furthermore, Gla residues are also found in pathologically mineralized soft tissues in the diseases of dermatomyositis, scleroderma and atherosclerosis, implicating vitamin K dependent calcium binding proteins in normal and pathological mineralization processes. To elucidate the function of osteocalcin in bone, the bone microsomal vitamin K carboxylase enzyme complex will be characterized and the endogenous microsomal substrate isolated after suitable incubation labelling the Gla protein by vitamin K dependent incorporation of 14CO2. The cellular origin of osteocalcin and its biosynthetic pathway in bone will be investigated. The identity of the Gla protein in ectopic calcifications by immunological methods and peptide mapping with other known Gla proteins and their de novo synthesis at the site of pathological calcifications will be pursued by assaying for vitamin K carboxylase activity. To determine if Gla has a general function in the mineralization of calcified cartilage, the vitamin k dependent calcium binding protein in the endoskeleton of elasmobranchs will be studied. The potential defect in bone mineralization as a result of vitamin K deficiency will be examined for by bone density fractionation as well as alterations in osteocalcin biosynthesis in defective mineralization induced by vitamin D deficiency. The turnover of vitamin K dependent proteins in growing children and patients with ectopic calcification and metabolic bone disorders will be assessed by measuring urine Gla excretion. The understanding of osteocalcin function in normal bone and the vitamin K dependent protein carboxylation system in pathological mineralization may provide an insight for the treatment and prevention of a variety of pathological conditions involving calcium deposition.